Iridium complex, OLED using the same, and nitrogen-containing tridentate ligand having carbene unit

ABSTRACT

An iridium complex and an OLED using the same are shown. The iridium complex is represented by formula (I), 
                         
wherein R 1  is substituted or unsubstituted C 1-12  alkyl, or substituted or unsubstituted C 6-12  aryl; R 2  is hydrogen, fluorine or —C m F 2m+1  (m=1, 2 or 3), substituted or unsubstituted C 1-12  alkyl, or substituted or unsubstituted C 6-12  aryl; R 3  is hydrogen, fluorine or —C m F 2m+1  (m=1, 2 or 3), substituted or unsubstituted C 1-6  alkyl or alkoxy, and n is 1, 2, 3 or 4; each of R 4  is hydrogen or substituted or unsubstituted C 1-12  alkyl, or R 4 &#39;s may join to form a C 3-8  aromatic ring, and R 4 &#39;s may be the same or different; X 1 , X 2 , X 3  and X 4  are each independently CH or nitrogen; Y 1 , Y 2  and Y 3  are each independently carbon or nitrogen, with a proviso that at least one of Y 1 , Y 2  and Y 3  is nitrogen, and the tridentate chelate Y 1 ^Y 2 ^Y 3  is dianionic.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority benefit of Taiwan applicationserial no. 104144592, filed on Dec. 31, 2015. The entirety of theabove-mentioned patent application is hereby incorporated by referenceherein and made a part of this specification.

BACKGROUND OF THE INVENTION

Field of Invention

The invention relates to an iridium complex for an organiclight-emitting diode (OLED), and more particularly, to an iridiumcomplex having a carbene fragment, an OLED using the iridium complex,and a nitrogen-containing tridentate chelate having a carbene unit thatis for forming the iridium complex.

Description of Related Art

OLED devices have got much attention in the display industry, especiallyin the flat display industry, as allowing low-voltage driving and havinghigh luminous efficiency.

In order to develop full-color flat displays, finding stable lightemitting materials with different colors and having high luminousefficiency is important in the research of OLED. So far certaintris-bidentate iridium complexes have been report to have suitableluminescence characteristics, but the rigidity and the stability thereofare often insufficient.

SUMMARY OF THE INVENTION

In view of the foregoing, the invention provides an iridium complexhaving a carbene fragment, which is capable of effectively increasingthe luminous efficiency when used in the light-emitting layer of anOLED.

The invention also provides an OLED adopting the iridium complex.

The invention further provides a nitrogen-containing tridentate chelatehaving a carbene unit that is for forming the iridium complex.

The iridium complex of the invention is represented by formula (I),

wherein R¹ is substituted or unsubstituted C₁₋₁₂ alkyl, or substitutedor unsubstituted C₆₋₁₂ aryl; R² is hydrogen, fluorine or —C_(m)F_(2m+1)(m=1, 2 or 3), substituted or unsubstituted C₁₋₁₂ alkyl, or substitutedor unsubstituted C₆₋₁₂ aryl; R³ is hydrogen, fluorine or —C_(m)F_(2m+1)(m=1, 2 or 3), substituted or unsubstituted C₁₋₆ alkyl, or substitutedor unsubstituted C₁₋₆ alkoxy, and n is 1, 2, 3 or 4; each of R⁴ ishydrogen or substituted or unsubstituted C₁₋₁₂ alkyl, or R⁴'s may jointo form a C₃₋₈ N-heteroaromatic or aromatic ring, and R⁴'s may be thesame or different; X¹, X², X³ and X⁴ are each independently CH ornitrogen; Y¹, Y² and Y³ are each independently carbon or nitrogen, witha proviso that at least one of Y¹, Y² and Y³ is nitrogen, and thetridentate chelate Y¹^Y²^Y³ is dianionic.

In an embodiment, Y¹ and Y² are nitrogen and Y³ is carbon, the iridiumcomplex being represented by formula (I-1)

wherein R¹, R², R³, R⁴, n, X¹, X², X³ and X⁴ are defined as above. It ispossible that X¹, X², X³ and X⁴ are all CH or that at least one of X¹,X², X³ and X⁴ is nitrogen.

The OLED of the invention includes two electrodes and a light-emittinglayer disposed between the two electrodes, wherein the light-emittinglayer contains the iridium complex of the invention. The iridium complexmay possibly function as a dopant in a host material of thelight-emitting layer.

The nitrogen-containing tridentate chelate having a carbene unit of theinvention is represented by formula (1),

wherein R¹, R², R³, R⁴, n, X¹, X², X³ and X⁴ are defined as above.

As compared to the conventional tris-bidentate iridium complexes, thebis-tridentate iridium complex of the invention has higher rigidity andstability, and therefore improves the luminous efficiency. The iridiumcomplex of the invention also has strong coordination bonding betweenmetal center and ligand so that the transition energy to themetal-centered dd excited states is raised and the non-radiativequenching of phosphorescence is reduced, thus improving the luminousefficiency and the color purity. In addition, the iridium complex of theinvention includes carbene as a strong-field ligand, which form strongerbonding with iridium so that the stability of the complex is higher.

In order to make the aforementioned and other objects, features andadvantages of the invention comprehensible, a preferred embodimentaccompanied with figures is described in detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the absorption spectra and the phosphorescence spectra ofthe carbene-containing iridium complexes synthesized in Examples 1 to 5of the invention.

FIG. 2 illustrates the OLED structure for measuring the luminescencecharacteristics of the iridium complexes in Example 7 of the invention.

DESCRIPTION OF EMBODIMENTS

The invention will be further explained with the following embodiments,which are just exemplary and are not intended to limit the scope of theinvention.

[Iridium Complex Having a Carbene Fragment]

The iridium complex having a carbene fragment of the invention isrepresented by formula (I),

wherein R¹ is substituted or unsubstituted C₁₋₁₂ alkyl, or substitutedor unsubstituted C₆₋₁₂ aryl; R² is hydrogen, fluorine or —C_(m)F_(2m+1)(m=1, 2 or 3), substituted or unsubstituted C₁₋₁₂ alkyl, or substitutedor unsubstituted C₆₋₁₂ aryl; R³ is hydrogen, fluorine or —C_(m)F_(2m+1)(m=1, 2 or 3), substituted or unsubstituted C₁₋₆ alkyl, or substitutedor unsubstituted C₁₋₆ alkoxy, and n is 1, 2, 3 or 4; each of R⁴ ishydrogen or substituted or unsubstituted C₁₋₁₂ alkyl, or R⁴'s may jointo form a C₃₋₈ N-heteroaromatic or aromatic ring, and R⁴'s may be thesame or different; X¹, X², X³ and X⁴ are each independently CH ornitrogen; Y¹, Y² and Y³ are each independently carbon or nitrogen, witha proviso that at least one of Y¹, Y² and Y³ is nitrogen, and thetridentate chelate Y¹^Y²^Y³ is dianionic.

The aromatic ring is an aromatic hydrocarbon ring or an aromaticheterocyclic ring. Specific examples of the aromatic ring include abenzene ring, a pyridine ring, a pyrazine ring, a pyrimidine ring, apyridazine ring, a triazine ring, a pyrrole ring, a furan ring, athiophene ring, a selenophene ring, a tellurophene ring, an imidazolering, a thiazole ring, a selenazole ring, a tellurazole ring, athiadiazole ring, an oxadiazole ring, and a pyrazole ring.

In an embodiment, R⁴'s may join to form a substituted or unsubstitutedbenzene ring or a substituted or unsubstituted pyridine ring.

The ligand at the right half of formula (I) is the nitrogen-containingtridentate chelate having a carbene unit of the invention that isrepresented by formula (1),

wherein R¹, R², R³, R⁴, n, X¹, X², X³ and X⁴ are defined as above.

The above tridentate chelate Y¹^Y²^Y³ may have at least oneelectron-withdrawing substituent. The tridentate chelate Y¹^Y²^Y³ may beselected from those known in the prior art. The highest occupiedmolecular orbital (HOMO) of the iridium complex of the invention isadjusted mainly with the tridentate chelate Y¹^Y²^Y³. The lowestunoccupied molecular orbital (LUMO) is adjusted mainly with thenitrogen-containing tridentate chelate having a carbene unit of theinvention that is represented by the aforementioned formula (1).

When Y¹ and Y² are nitrogen and Y³ is carbon, the iridium complex isrepresented by formula (I-1),

wherein R¹, R², R³, R⁴, n, X¹, X², X³ and X⁴ are defined as in the caseof formula (I).

R² is hydrogen, fluorine or —C_(m)F_(2m+1) (m=1, 2 or 3), substituted orunsubstituted C₁₋₁₂ alkyl, or substituted or unsubstituted C₆₋₁₂ aryl;R³ may be hydrogen, fluorine or —C_(m)F_(2m+1) (m=1, 2 or 3),substituted or unsubstituted C₁₋₆ alkyl, or substituted or unsubstitutedC₁₋₆ alkoxy, and n is 1, 2, 3 or 4. When R³ is C₁₋₆ alkyl, fluorine or—C_(m)F_(2m+1) and X¹, X², X³ and X⁴ are all CH, specific examples ofthe iridium complexes satisfying formula (I-1) include the followingiridium complexes represented by formulas (I-1-1), (I-1-2), (I-1-3),(I-1-4), (I-1-5), (I-1-6) . . . (I-1-24), respectively, abbreviated ascompounds (I-1-1), (I-1-2), . . . hereinafter. The abbreviation rulealso applies to the later described iridium complexes represented byother chemical structures.

When R³ is C₁₋₆ alkyl, C₁₋₆ alkoxyl, fluorine or —C_(m)F_(2m+1) and atleast one of X¹, X², X³ and X⁴ is nitrogen, specific examples of theiridium complexes satisfying formula (I-1) included the followingiridium complexes represented by formulas (I-1-25), (I-1-26) . . .(I-1-31), respectively. These iridium complexes all have at least one ofX¹, X², X³ and X⁴ being nitrogen, and the design of X² and/or X⁴ beingnitrogen thereof is capable of increasing the electron-withdrawingeffect of the nitrogen-containing tridentate chelate represented byformula (1).

In addition, a case where Y¹, Y² and Y³ in the tridentate chelateY¹^Y²^Y³ are all nitrogen and a case where Y¹ and Y³ are carbon and Y²is nitrogen are both feasible. Specific examples of the latter case areprovided below.

The OLED of the invention includes two electrodes and a light-emittinglayer disposed therebetween. The light-emitting layer contains the aboveiridium complex having a carbene fragment. The material of each of thetwo electrodes can be selected from commonly used materials in thefield, and other functional layers, such as an electron transportationlayer and a hole transportation layer, can also be disposed between theelectrodes and the light-emitting layer using a known technique in theart. The OLED may be fabricated on a substrate, such as a glasssubstrate.

[Forming Method of the Iridium Complex Having a Carbene Fragment]

The nitrogen-containing tridentate chelate having a carbene unit of theinvention is, for instance, obtained by removing two protons from aprecursor thereof. A specific example is shown below, wherein “phimpy”and “phimpy-H₂” are symbols used in this specification, “Bu^(t)”represents t-butyl, and “Pr^(i)” represents isopropyl.

The precursor phimpy-H₂ in the above specific example may be preparedwith the following method, wherein step (i) uses imidazole,tetrabutylammonium bromide (NBu₄Br) and potassium hydroxide as reagents,step (ii) uses 2,4-difluorophenylboronic acid, Pd(dppf)Cl₂ and KHCO₃ asreagents, step (iii) uses 2-iodopropane as a reagent, and step (iv) usesNH₄PF₆ as a reagent.

The tridentate chelate Y¹^Y²^Y³ in the iridium complex represented byformula (I) may be formed by mixing and reacting a precursor having acorresponding ring structure with a necessary reagent.

The iridium complex having a carbene fragment of the invention can beprepared by adopting suitable reactants and reaction conditionsaccording to the change of each chelate, and the reaction preparationmethod can be modified based on known techniques in the art. A specificexample of the preparation method of the iridium complex contains thefollowing steps. The precursor of the nitrogen-containing tridentatechelate represented by formula (1) of the invention, an iridium source,and other required reagent(s) are mixed, and then the obtained product,a precursor of the tridentate chelate Y¹^Y²^Y³, and other requiredreagent(s) are mixed, and a reaction was caused by heating. The order inwhich the nitrogen-containing tridentate chelate represented by formula(1) and the tridentate chelate Y¹^Y²^Y³ are bonded to the iridium atomcan be reversed. That is, the iridium atom and the precursor of thetridentate chelate Y¹^Y²^Y³ are reacted first, and then the product andthe precursor of the nitrogen-containing tridentate chelate representedby formula (1) are reacted.

EXAMPLE

Certain examples are provided below to further describe the invention,which are merely exemplary and are not intended to limit the scope ofthe invention.

Synthesis Example 1: Preparation of the Precursor Phimpy-H₂ of theNitrogen-Containing Tridentate Chelate Represented by Formula (1)

A mixture of 4-(t-butyl)-2,6-dichloropyridine (1.3 g, 6.37 mmol),imidazole (0.48 g, 7.01 mmol), tetrabutylammonium bromide (1.03 g, 3.18mmol) and potassium hydroxide (0.43 g, 7.64 mmol) were put in a one-neckflask and then reacted at 80° C. for 12 hours. The obtained imidazoliumintermediate was subsequently reacted with 2,4-difluorophenylboronicacid (0.88 g, 5.60 mmol), Pd(dppf)Cl₂ (0.11 g, 0.15 mmol), and KHCO₃(2.07 g, 15.00 mmol) in a mixture of toluene (15 mL), ethanol (3 mL),and water (3 mL). The reaction mixture was heated at 110° C. for 12hours to form4-(t-butyl)-2-(2,4-difluorophenyl)-6-(1H-imidazol-1-yl)pyridine.

The obtained product (1.15 g, 3.68 mmol) and 2-iodopropane (0.8 mL, 8.07mmol) were dissolved in toluene (40 mL) and then heated at 110° C. for12 hours to form an imidazolium iodide pre-ligand. The obtainedimidazolium iodide pre-ligand (1.5 g, 3.1 mmol) and NH₄PF₆ (4.04 g, 25mmol) were dissolved in ethanol and stirred for 2 hours to perform ionexchange. Addition of water resulted in the precipitation of(phimph-H₂)(PF₆).

Spectral data of (phimph-H₂)(PF₆): ¹H NMR (400 MHz, CDCl₃): δ 9.53 (s,1H), 8.24 (s, 1H), 8.01-7.95 (m, 1H), 7.88 (s, 1H), 7.81 (s, 1H), 7.48(s, 1H), 7.06-7.02 (m, 1H), 6.97-6.92 (m, 1H), 4.99-4.96 (m, 1H, CH),1.59 (d, J=6.6 Hz, 3H, Me), 1.58 (d, J=6.6 Hz, 3H, Me), 1.42 (s, 9H,t-Bu). ¹⁹F NMR (376 MHz, CDCl₃): δ −70.90 (d, J=712 Hz, PF₆), −107.10(s, 1F), −111.65 (s, 1F).

Example 1: Preparation of Compound (I-1-7)

[Ir(COD)(μ-Cl)]₂ (300 mg, 0.45 mmol), (phimph-H₂)(PF₆) (470 mg, 0.94mmol) and NaOAc (183 mg, 2.23 mmol) were put in a two-neck flask andreacted at 80° C. for 12 hours, using anhydrous acetonitrile (20 mL) asa solvent. After the temperature was lowered to room temperature and thesolvent was evaporated,2-(5-trifluoromethyl-1H-pyrazol-3-yl)-6-(4-fluorophenyl)pyridine (316mg, 1.03 mmol) and sodium acetate (366 mg, 4.47 mmol) were added, andthe mixture was dissolved in decahydronaphthalene (20 mL) and reacted at200° C. for 24 hours. After the reaction was finished, purification wasdone by column chromatography to obtain a product (yield: 23%).

Spectral data of compound (I-1-7): ¹H NMR (400 MHz, CDCl₃): δ 8.14 (s,1H), 7.76 (t, J=8.0 Hz, 1H), 7.60-7.55 (m, 4H), 7.37 (s, 1H), 6.91 (s,1H), 6.79 (d, J=2.4 Hz, 1H), 6.56-6.51 (m, 1H), 6.32-6.26 (m, 1H), 5.53(d, J=8.0 Hz, 2H), 3.53-3.29 (m, 1H, CH), 1.54 (s, 9H, t-Bu), 0.80 (d,J=6.8 Hz, 3H, Me), 0.74 (d, J=6.8 Hz, 3H, Me). ¹⁹F NMR (376 MHz, CDCl₃):δ −59.81 (s, 3F), −107.49 (d, J=9.8 Hz, 1F), −110.48 (d, J=9.8 Hz, 1F),110.52 (s, 1F). MS [FAB]: m/z 852.6, M⁺. Anal. Calcd. for C₃₆H₂₉F₆IrN₆:C, 50.76; H, 3.43; N, 9.87. Found: C, 50.64; H, 3.77; N, 9.48.

Example 2: Preparation of Compound (I-1-8)

The synthesis steps of compound (I-1-8) was similar to those of compound(I-1-7), except that2-(5-trifluoromethyl-1H-pyrazol-3-yl)-6-(4-fluorophenyl)pyridine wasreplaced by2-(5-trifluoromethyl-1H-pyrazol-3-yl)-6-(4-trifluoromethylphenyl)pyridine.The yield of compound (I-1-8) was 26%.

Spectral data of compound (I-1-8): ¹HNMR (400 MHz, CDCl₃): δ 8.15 (s,1H), 7.81 (t, J=8.0 Hz, 1H), 7.72 (d, J=8.0 Hz, 1H), 7.67 (d, J=8.0 Hz,1H), 7.64 (d, J=8.0 Hz, 1H), 7.58 (s, 1H), 7.39 (s, 1H), 7.05 (d, J=8.0Hz, 1H), 6.93 (s, 1H), 6.81 (s, 1H), 6.33-6.27 (m, 1H), 6.05 (s, 1H),5.49 (s, 1H), 3.33-3.27 (m, 1H, CH), 1.53 (s, 9H, t-Bu), 0.80 (d, J=6.8Hz, 3H, Me), 0.74 (d, J=6.8 Hz, 3H, Me). ¹⁹F NMR (376 MHz, CDCl₃): δ−59.89 (s, 3F), −62.81 (s, 3F), −107.42 (d, J=9.8 Hz, 1F), −110.35 (d,J=9.8 Hz, 1F). MS [FAB]: m/z 902.7, M. Anal. Calcd. for C₃₇H₂₉F₈IrN₆: C,49.28; H, 3.24; N, 9.32. Found: C, 49.29; H, 3.33; N, 8.91.

Example 3: Preparation of Compound (I-1-9)

IrCl₃.3H₂O (200 mg, 0.57 mmol) and (phimph-H₂)(PF₆) (313 mg, 0.62 mmol)were put in a one-neck flask and reacted at 120° C. for 12 hour, using2-methoxyethanol (15 mL) as a solvent, and then the temperature waslowered to room temperature. After the solvent was evaporated,2-(5-trifluoromethyl-1H-pyrazol-3-yl)-6-(4-t-butylphenyl)pyridine (215mg, 0.62 mmol) and NaOAc (209 mg, 2.55 mmol) were added, and the mixturewas dissolved in decahydronaphthalene (20 mL) and reacted at 200° C. for24 hours. After the reaction was finished, purification was done bycolumn chromatography to obtain a product (yield: 23%).

Spectral data of compound (I-1-9): ¹H NMR (400 MHz, CDCl₃): δ 8.13 (s,1H), 7.72 (t, J=8.0 Hz, 1H), 7.59-7.56 (m, 3H), 7.46-7.44 (m, 2H), 6.92(s, 1H), 6.82 (dd, J=8.0 Hz, 2.0 Hz, 1H), 6.73 (d, J=2.0 Hz, 1H),6.30-6.24 (m, 1H), 5.64 (d, J=2.0 Hz, 1H), 5.60 (dd, J=8.0 Hz, 2.0 Hz,1H), 3.39-3.32 (m, 1H), 1.50 (s, 9H, t-Bu), 0.92 (s, 9H, t-Bu), 0.81 (d,J=6.8 Hz, 3H, Me), 0.69 (d, J=6.8 Hz, 3H, Me). ¹⁹F NMR (376 MHz, CDCl₃):δ −59.77 (s, 3F), 107.80 (d, J=9.8 Hz, 1F), −111.36 (d, J=9.8 Hz, 1F).MS [FAB]: m/z, 890.7 M⁺.

Example 4: Preparation of Compound (I-1-10)

The synthesis steps of compound (I-1-10) was similar to those ofcompound (I-1-7), except that2-(5-trifluoromethyl-1H-pyrazol-3-yl)-6-(4-fluorophenyl)pyridine wasreplaced by2-(5-trifluoromethyl-1H-pyrazol-3-yl)-6-(1-naphthyl)pyridine. The yieldof compound (I-1-10) was 35%.

Spectral data of compound (I-1-10): ¹HNMR (400 MHz, CDCl₃): δ 8.61 (d,J=8.0 Hz, 1H), 8.38 (d, J=8.0 Hz, 1H), 8.17 (s, 1H), 7.82 (t, J=8.0 Hz,1H), 7.65-7.60 (m, 2H), 7.56 (d, J=2.0 Hz, 1H), 7.48 (t, J=8 Hz, 1H),7.41 (s, 1H), 7.28 (t, J=8.0 Hz, 1H), 7.10 (d, J=8.0 Hz, 1H), 6.94 (s,1H), 6.73 (d, J=2.0 Hz, 1H), 6.28-6.22 (m, 1H), 6.11 (d, J=8.0 Hz, 1H)5.45 (d, J=8.0 Hz, 1H), 3.45-3.39 (m, 1H, CH), 1.55 (s, 1H, t-Bu), 0.76(d, J=6.8 Hz, 3H, Me), 0.73 (d, J=6.8 Hz, 3H, Me). ¹⁹F NMR (376 MHz,CDCl₃): δ −59.75 (s, 3F), −107.24 (d, J=9.8 Hz, 1F), −110.65 (d, J=9.8Hz, 1F). MS [FAB]: m/z, 884.5 M. Anal. Calcd. for C₄₀H₃₂F₅IrN₆: C,54.35; H, 3.65; N, 9.51. Found: C, 54.26; H, 4.06; N, 8.90.

Example 5: Preparation of Compound (I-1-11)

[Ir(COD)(μ-Cl)]₂ (118 mg, 0.18 mmol), (phimph-H₂)(PF₆) (186 mg, 0.37mmol) and NaOAc (72 mg, 0.88 mmol) were put in a two-neck flask andreacted at 80° C. for 12 hours, using anhydrous acetonitrile (10 mL) asa solvent. After the temperature was lowered to room temperature and thesolvent was evaporated,2-(5-trifluoromethyl-1H-pyrazol-3-yl)-6-phenylisoquinoline (120 mg, 0.36mmol) and NaOAc (144 mg, 1.76 mmol) were added, and the mixturedissolved in xylene (25 mL) and reacted at 160° C. for 24 hours. Afterthe reaction was finished, purification was done by columnchromatography to obtain a product (yield: 27%).

Spectral data of compound (I-1-11): ¹HNMR (400 MHz, CDCl₃): δ 8.95 (d,J=8.0 Hz, 1H), 8.32 (d, J=8.0 Hz, 1H), 8.14 (s, 1H), 8.05 (d, J=7.6 Hz,1H), 7.98 (s, 1H), 7.73-7.67 (m, 2H), 7.56 (d, J=2.0 Hz, 1H), 7.39 (s,1H), 6.94 (s, 1H), 6.93 (t, J=6.8 Hz, 1H), 6.75 (d, J=2.0 Hz, 1H), 6.71(t, J=7.6 Hz, 1H), 6.28-6.22 (m, 1H), 6.06 (d, J=6.8 Hz, 1H), 5.45 (m,1H), 3.34-3.27 (m, 1H, CH), 1.54 (s, 9H, t-Bu), 0.72 (d, J=6.8 Hz, 3H,Me), 0.66 (d, J=6.8 Hz, 3H, Me). ¹⁹F NMR (376 MHz, CDCl₃): δ −59.65 (s,3F), −107.69 (d, J=9.8 Hz, 1F), −110.85 (d, J=9.8 Hz, 1F). MS [FAB]:m/z, 884.3 M⁺.

Example 6: Preparation of Compound (I-1-13)

[Ir(COD)(μ-Cl)]₂ (50 mg, 0.07 mmol), (phimph-H₂)(PF₆) (75 mg, 0.15 mmol)and NaOAc (62 mg, 0.76 mmol) were put in a two-neck flask and reacted at80° C. for 12 hours, using anhydrous acetonitrile (10 mL) as a solvent.After the temperature was lowered to room temperature and the solventwas evaporated,4-tert-butyl-2-phenyl-6-(3-(trifluoromethyl)-1H-5-pyrazolyl) pyrimidine(52 mg, 0.15 mmol) and NaOAc (144 mg, 1.76 mmol) were added, and themixture dissolved in xylene (25 mL) and reacted at 160° C. for 24 hours.After the reaction was finished, purification was done by columnchromatography to obtain a product (yield: 31%).

Spectral data of compound (I-1-13): ¹HNMR (400 MHz, CDCl₃): δ 8.14 (s,1H), 8.04 (d, J=7.4 Hz, 1H), 7.54 (s, 1H), 7.51 (s, 1H), 7.36 (s, 1H),7.07 (s, 1H), 6.87 (t, J=7.4 Hz, 1H), 6.77-6.72 (m, 2H), 6.28 (t, J=9.6Hz, 1H), 5.86 (d, J=7.4 Hz, 1H), 5.54 (dd, J=3.8, 2.2 Hz, 1H), 3.29-3.22(m, 1H, CH), 1.53 (s, 9H, t-Bu), 0.72 (d, J=6.8 Hz, 3H, Me), 0.66 (d,J=6.8 Hz, 3H, Me); ¹⁹F NMR (376 MHz, CDCl₃): δ −59.92 (s, 3F), −107.51(d, J=9.8 Hz, 1F), −110.57 (d, J=9.8 Hz, 1F); MS [FAB]: m/z, 891.3 M.

The absorption spectra and the phosphorescence spectra of the iridiumcomplexes (I-1-7) to (I-1-11) that were synthesized in Examples 1 to 5are shown in FIG. 1, and the absorption peak location (abs λ_(abs)), theemission peak location (λ_(em)), the quantum yield (ϕ), and thephosphorescence lifetime (τ) thereof are listed in Table 1 below.

Com- ϕ τ_(obs)/ pound λ_(abs)/nm (ε × 10⁴ M⁻¹cm⁻¹)^(a) λ_(em)/nm^(b)(%)^(b, c) μs^(b) (I-1-7) 304 (2.25), 340 (1.77), 398 (0.38) 473, 508 993.10 (I-1-8) 311 (2.1), 350 (1.40), 410 (0.34) 495, 534, 91 3.91 574(sh) (I-1-9) 310 (2.53), 343 (1.81), 408 (0.44) 481, 515 ~100 3.01(I-1-10) 330 (2.38), 430 (0.4), 458 (0.31) 583, 618 25 9.23 (I-1-11) 345(2.64), 448 (0.60), 481 (0.29) 608, 663, 57 5.40 725 (sh) ^(a)Measuredin CH₂Cl₂ in a concentration of 10⁻⁵ M. ^(b)Measured in degassed CH₂Cl₂solution. ^(c) Coumarin (C153) in EtOH (Φ = 58% and λ_(max) = 530 nm)and 4-(dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4H-pyran inDMSO (Φ = 80% and λ_(max) = 637 nm) were employed as standard.

It is clear from FIG. 1 and Table 1 that compounds (I-1-7), (I-1-8) and(I-1-9) have high quantum yields, and compounds (I-1-10) and (I-1-11) inwhich the tridentate chelate C^N^N′ further include a benzo-ring canenhance conjugation of the chromophore to reduce the energy gap and makea red shift of the emitted light.

Other effects of the above compounds are described below. As compared tothe N—Ir bonding formed by coordination of a pyridine ligand to iridium,the C—Ir bonding formed by coordination of carbene as a strong-fieldligand to iridium is stronger, so that the stability of the complex ishigher. Regarding the luminous performance, the strong coordinationbonding can raise the transition energy to the metal-centered dd excitedstates and to reduce the non-radiative quenching of phosphorescence,thus improving the luminous efficiency and the color purity. Inaddition, as compared to the conventional tris-bidentate iridiumcomplexes, the bis-tridentate iridium complex of the invention hashigher rigidity, and therefore improves the luminous efficiency and thedevice stability.

Example 7

An OLED was fabricated using one of the iridium complexes of theinvention. The structure thereof was schematically illustrated in FIG.2, including a glass substrate 200, an anode 202, a hole transportationlayer 204, a light-emitting layer 206, an electron transportation layer208 and a cathode 210. The material of the anode 202 is ITO. Thematerial of the hole transportation layer 204 is TAPC. The material ofthe light-emitting layer 206 is mCP doped with the iridium complex ofthe invention. The material of the electron transportation layer 208 isTmPyPB. The material of the cathode 210 is LiF/Al.

As mentioned above, the iridium complex of the invention has strongcoordination bonding so that the transition energy to the metal-centereddd excited states is raised and the non-radiative of phosphorescence isreduced, thus improving the luminous efficiency and the color purity. Inaddition, the iridium complex of the invention includes carbene as astrong-field ligand, which form stronger bonding with iridium so thatthe stability of the complex is higher.

The invention has been disclosed above in the preferred embodiments, butis not limited to those. It is known to persons skilled in the art thatsome modifications and innovations may be made without departing fromthe spirit and scope of the invention. Hence, the scope of the inventionshould be defined by the following claims.

What is claimed is:
 1. An iridium complex, being represented by formula(I):

wherein R¹ is substituted or unsubstituted C₁₋₁₂ alkyl, or substitutedor unsubstituted C₆₋₁₂ aryl; R² is hydrogen, fluorine or —C_(m)F_(2m+1)(m=1, 2 or 3), substituted or unsubstituted C₁₋₁₂ alkyl, or substitutedor unsubstituted C₆₋₁₂ aryl; R³ is hydrogen, fluorine or —C_(m)F_(2m+1)(m=1, 2 or 3), substituted or unsubstituted C₁₋₆ alkyl, or substitutedor unsubstituted C₁₋₆ alkoxy, and n is 1, 2, 3 or 4; each of R⁴ ishydrogen or substituted or unsubstituted C₁₋₁₂ alkyl, or R⁴'s may jointo form a C₃₋₈ N-heteroaromatic or aromatic ring, and R⁴'s may be thesame or different; X¹, X², X³ and X⁴ are each independently CH ornitrogen; Y¹ is nitrogen in a pyrazole ring as a part of the tridentatechelate Y¹^Y²^Y³, Y² and Y³ are each independently carbon or nitrogen,and the tridentate chelate Y¹^Y²^Y³ is dianionic.
 2. The iridium complexof claim 1, wherein the tridentate chelate Y¹^Y²^Y³ has at least oneelectron-withdrawing substituent.
 3. The iridium complex of claim 1,wherein is nitrogen and Y³ is carbon, the iridium complex beingrepresented by formula (I-1):

wherein R¹, R², R³, R⁴, n, X¹, X², X³ and X⁴ are defined as in claim 1.4. The iridium complex of claim 1, wherein X¹, X², X³ and X⁴ are all CH.5. The iridium complex of claim 4, being represented by any one offormulae (I-1-1) to (I-1-24):


6. The iridium complex of claim 1, wherein at least one of X¹, X², X³and X⁴ is nitrogen.
 7. The iridium complex of claim 6, being representedby any one of formulae (I-1-25) to (I-1-31):


8. The iridium complex of claim 1, having a structure represented by oneof formulae (I-a) and (I-b):


9. An organic light-emitting diode, comprising two electrodes and alight-emitting layer disposed between the two electrodes, wherein thelight-emitting layer contains the iridium complex of claim
 1. 10. Theorganic light-emitting diode of claim 9, wherein the iridium complexfunctions as a dopant in a host material of the light-emitting layer.11. An N-containing tridentate chelate having a carbene unit,represented by formula (1):

wherein R¹ is substituted or unsubstituted C₁₋₁₂ alkyl, or substitutedor unsubstituted C₆₋₁₂ aryl; R² is hydrogen, fluorine or —C_(m)F_(2m+1)(m is 1, 2 or 3), substituted or unsubstituted C₁₋₁₂ alkyl, orsubstituted or unsubstituted C₆₋₁₂ aryl; R³ is hydrogen, fluorine or—C_(m)F_(2m+1) (m=1, 2 or 3), substituted or unsubstituted C₁₋₆ alkyl,or substituted or unsubstituted C₁₋₆ alkoxy, and n is 1, 2, 3 or 4; eachof R⁴ is hydrogen or substituted or unsubstituted C₁₋₁₂ alkyl, or R⁴'smay join to form a C₃₋₈ N-heteroaromatic or aromatic ring, and R⁴'s maybe the same or different; X¹, X², X³ and X⁴ are each independently CH ornitrogen, wherein at least one of X¹, X², X³ and X⁴ is nitrogen.